SEASONAL OCCURRENCE OF PICOCYANOBACTERIA IN THE GREENLAND SEA AND CENTRAL ARCTIC-OCEAN

The seasonal occurrence of picocyanobacteria in the Greenland Sea and Arctic Ocean was investigated during four expeditions in May-June 1987 and 1988, August-October 1991, and November-December 1988 by epifluor escence microscopy. In early summer, the abundance of picocyanobacteri a was related to water masses: they were nearly absent in polar water, whereas they occurred in high concentrations (up to 5470 cells ml(-1) ) in Atlantic Water. During autumn and beginning of winter, the abunda nces of picocyanobacteria remained around 10(3) cells ml(-1). Their re lative contribution to total picoplanktonic algal abundance increased from 0% during spring/summer to 70-80% in late autumn, as a result of a decrease in the abundance of eucaryotic picoalgae. Consequently, the impact of picocyanobacteria on Arctic epipelagic carbon and energy fl ow is of minor importance, and the strong contribution of picoplankton algae to biomass and primary productivity in Arctic seas has to be at tributed to eucaryotic species.